Conventional aviation and aerospace fuel tank coatings, such as BMS10-39, may be degraded by certain fuel additives such as DIEGME. At elevated concentrations, DIEGME may chemically degrade conventional epoxy-based fuel tank paints or coatings, resulting in peeling of the topcoat. Such chemical degradation of conventional epoxy-based paints or coatings poses particular problems in aerospace or aviation applications, such as military aircraft, where DIEGME may be present in jet fuel or jet propellant (JP). DIEGME may be added to jet fuel or JP as a fuel system icing inhibitor (FSII), which prevents or reduces the buildup of ice inside of the fuel tank that may otherwise result from the low temperatures experienced due to aircraft operation in cold weather or at high altitude. For example, JP-5 and JP-8 are military jet fuels that typically include DIEGME as a FSII. Similarly, DIEGME may also be added to Jet A or Jet A-1 fuels as a FSII.
During normal aircraft operation, the DIEGME present in jet fuel may condense on the head space of the fuel tank in elevated concentrations, and/or it may become enriched in the residual water that may reside on the bottom of the fuel tank. At these elevated concentrations, DIEGME may act as a solvent for conventional epoxy-based fuel tank paints or coatings, which may result in topcoat swelling and/or peeling. Peeled fuel tank topcoat creates a dangerous operating condition for the aircraft as the peeled topcoat may enter and clog the fuel filter, thereby disrupting operation of the fuel system.
Fuel tank topcoat peeling problems resulting from the presence of DIEGME in jet fuel have been reported in United States Air Force (USAF) aircraft such as the B-52, KC-135, and C-17. Similar problems have been reported in United States Navy aircraft such as the P-3. Accordingly, there is a need for DIEGME resistant fuel tank coatings.
Additionally, Jet fuel contains microorganisms that consume plastic and rubber components of the aircraft fuel system, and produce acidic metabolic byproducts. Conventional epoxy-based coating compositions that include an amine-based curing system exhibit acceptable adhesion, but do not provide sufficient acid resistance and/or microbial byproducts resistance. Conversely, conventional coating compositions that include a polyurethane-based curing system exhibit acceptable acid and microbial byproducts resistance, but do not provide sufficient adhesion to a substrate, especially direct adhesion to a metal substrate. Accordingly, there is a need for coating compositions that have low temperature flexibility and good adhesion to a substrate, as well as resistance to DIEGME, fuel, methyl ethyl ketone, and microbial byproducts.